1. Field of the Invention
The present invention relates to a radar apparatus configured to increase its detection sensitivity by emitting a transmission wave multiple times in the same direction. The radar apparatus of the present invention can be mounted on a vehicle to detect a traveling-ahead vehicle, or an obstacle.
2. Description of Related Art
As described, for example, in Japanese Patent Application Laid-open No. 8-313631, there is known such a radar apparatus used as a light wave distance meter that is configured to transmit a pulsed light, receive the pulsed light reflected from a measurement object, and determine a distance to the measurement object on the basis of a time difference between a moment of emission of the pulsed light and a moment of reception of the reflected pulsed light.
The distance measuring method in such conventional radar is explained in more detail below. First, a light emitting means emits a pulsed light when it is driven by a light emission timing signal. This pulsed light is reflected from the measurement object, and received by a light receiving means where it is converted into a light reception pulse signal having a signal level depending on the intensity of this received pulsed light. This light reception pulse signal is A/D converted in a predetermined sampling cycle. And a set of digital data signals resulting from this A/D conversion, which represent a waveform of the received pulsed light, are stored in a memory circuit. The light emitting means emits the pulsed light multiple times in order to average the digital data signals stored in the memory. A distance to the measurement object can be determined by referring to the digital data signals stored in the memory.
By emitting the pulsed light multiple times to integrate the digital data signals stored in the memory, it is possible to improve the detection sensitivity of the radar apparatus. Accordingly, the above described radar apparatus can accurately measure the distance to the measurement object even when the reception intensity of each individual reflected pulsed light is weak.
However, the reception intensity of the reflected pulsed light varies depending on the reflectivity of the measured object, and the distance to the measured object. Accordingly, such a conventional radar apparatus described above, which is configured to always emit the pulsed light a predetermined number of times, has a problem in that even when the reception intensity of each individual reflected pulsed light is strong, and accordingly the distance measurement can be performed by a fewer number of times of emitting the pulsed light, it always uselessly emits the pulsed light by the predetermined number of times. This may promote degradation of a light source of the pulsed light, and delay detection of the measured object.